net: Add back alignment for size for __alloc_skb
Commit
87fb4b7b533073eeeaed0b6bf7c2328995f6c075 (net: more
accurate skb truesize) changed the alignment of size. This
can cause problems at least on some machines with NFS root:
Unhandled fault: alignment exception (0x801) at 0xc183a43a
Internal error: : 801 [#1] PREEMPT
Modules linked in:
CPU: 0 Not tainted (
3.1.0-08784-g5eeee4a #733)
pc : [<
c02fbba0>] lr : [<
c02fbb9c>] psr:
60000013
sp :
c180fef8 ip :
00000000 fp :
c181f580
r10:
00000000 r9 :
c044b28c r8 :
00000001
r7 :
c183a3a0 r6 :
c1835be0 r5 :
c183a412 r4 :
000001f2
r3 :
00000000 r2 :
00000000 r1 :
ffffffe6 r0 :
c183a43a
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
Control:
0005317f Table:
10004000 DAC:
00000017
Process swapper (pid: 1, stack limit = 0xc180e270)
Stack: (0xc180fef8 to 0xc1810000)
fee0:
00000024 00000000
ff00:
00000000 c183b9c0 c183b8e0 c044b28c c0507ccc c019dfc4 c180ff2c c0503cf8
ff20:
c180ff4c c180ff4c 00000000 c1835420 c182c740 c18349c0 c05233c0 00000000
ff40:
00000000 c00e6bb8 c180e000 00000000 c04dd82c c0507e7c c050cc18 c183b9c0
ff60:
c05233c0 00000000 00000000 c01f34f4 c0430d70 c019d364 c04dd898 c04dd898
ff80:
c04dd82c c0507e7c c180e000 00000000 c04c584c c01f4918 c04dd898 c04dd82c
ffa0:
c04ddd28 c180e000 00000000 c0008758 c181fa60 3231d82c 00000037 00000000
ffc0:
00000000 c04dd898 c04dd82c c04ddd28 00000013 00000000 00000000 00000000
ffe0:
00000000 c04b2224 00000000 c04b21a0 c001056c c001056c 00000000 00000000
Function entered at [<
c02fbba0>] from [<
c019dfc4>]
Function entered at [<
c019dfc4>] from [<
c01f34f4>]
Function entered at [<
c01f34f4>] from [<
c01f4918>]
Function entered at [<
c01f4918>] from [<
c0008758>]
Function entered at [<
c0008758>] from [<
c04b2224>]
Function entered at [<
c04b2224>] from [<
c001056c>]
Code:
e1a00005 e3a01028 ebfa7cb0 e35a0000 (
e5858028)
Here PC is at __alloc_skb and &shinfo->dataref is unaligned because
skb->end can be unaligned without this patch.
As explained by Eric Dumazet <eric.dumazet@gmail.com>, this happens
only with SLOB, and not with SLAB or SLUB:
* Eric Dumazet <eric.dumazet@gmail.com> [111102 15:56]:
>
> Your patch is absolutely needed, I completely forgot about SLOB :(
>
> since, kmalloc(386) on SLOB gives exactly ksize=386 bytes, not nearest
> power of two.
>
> [ 60.305763] malloc(size=385)->
ffff880112c11e38 ksize=386 -> nsize=2
> [ 60.305921] malloc(size=385)->
ffff88007c92ce28 ksize=386 -> nsize=2
> [ 60.306898] malloc(size=656)->
ffff88007c44ad28 ksize=656 -> nsize=272
> [ 60.325385] malloc(size=656)->
ffff88007c575868 ksize=656 -> nsize=272
> [ 60.325531] malloc(size=656)->
ffff88011c777230 ksize=656 -> nsize=272
> [ 60.325701] malloc(size=656)->
ffff880114011008 ksize=656 -> nsize=272
> [ 60.346716] malloc(size=385)->
ffff880114142008 ksize=386 -> nsize=2
> [ 60.346900] malloc(size=385)->
ffff88011c777690 ksize=386 -> nsize=2
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>